Semiconductor memory circuit

ABSTRACT

The present invention provides a semiconductor memory circuit capable of reducing current consumption at non-operation in a system equipped with a plurality of chips that share the use of a power supply, address signals and a data bus. The semiconductor memory circuit has an internal circuit which is capable of selectively performing the supply and stop of an operating voltage via switch means and includes a memory array. An input circuit, which receives a predetermined control signal therein, controls the supply and stop of the operating voltage by the switch means to reduce a DC current and a leak current when no memory operation is done, whereby low power consumption can be realized.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 11/174,604 filed Jul. 6, 2005, which is now U.S. Pat. No. 7,088,636,which is a Continuation application of U.S. application Ser. No.10/190,480 filed on Jul. 9, 2002, which is now U.S. Pat. No. 6,934,210.Priority is claimed based upon U.S. application Ser. No. 11/174,604filed Jul. 6, 2005, which claims the priority of U.S. application Ser.No. 10/190,480 filed on Jul. 9, 2002, which claims the priority date ofJapanese Application No. 2001-261123 filed on Aug. 30, 2001, and whichis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates mainly to a semiconductor memory circuitwhich needs a refresh operation, and to a technology effective forapplication to a pseudo static RAM or the like usable equally to astatic RAM (Random Access Memory) equivalently.

A so-called DRAM of a time multiplex system wherein in order to make itpossible to cope with a DRAM in a manner similar to an SRAM (StaticRandom Access Memory), a read/write operation and a refresh operationare executed during one cycle with their times being allocated therefor,or the two operations are performed only when the read/write operationand the refresh operation compete with each other, has been proposed inUnexamined Patent Publication No. Sho 61(1986)-71494.

SUMMARY OF THE INVENTION

In the DRAM including the time multiplex system referred to above, a DCcurrent in an internal power supply circuit mounted in a chip, and arefresh current for data retention are consumed even when the chip isnon-operated (at standby) in a state in which an external power supplyVDD is being applied. Further, an off current of each MOSFET is used upor consumed even in a state in which a CMOS logic circuit constituting aperipheral circuit is deactivated. This off current results from asubthreshold characteristic of the MOSFET. Even if a gate voltage is offat 0V in the case of an N channel MOSFET, for example, a small offcurrent flows between its drain and source. In the case of a DRAM havingmemory capacity like about 32 M(Mega) bits, for example, an off currentat its entirety is innegligible.

When a DRAM chip is mounted to a system, other memory chips (e.g., ROM,etc.) and power supplies VDD and VSS, and external signals (addresssignal Ai and data bus DQ) are shared. Even when the DRAM chip isdeactivated (at standby) in this case, it is necessary to apply thepower supplies VDD and VSS for the purpose of a memory access to a ROMchip. Thus, even when the DRAM chip is in the above-deactivated state,it continues to allow current consumption to flow uselessly.

For example, a DRAM used in a portable device or the like operated bybattery driving needs a reduction in at-standby current in a broadtemperature region. As the at-standby currents in the DRAM, may bementioned, a DC current consumed by a power supply circuit or the like,the off current of each MOSFET, and the refresh operating current fordata retention. Since the occupied rate of off current of these currentsis large in the neighborhood of the maximum operation compensatingtemperature, the adoption or the like of an off-current cut MOSFET (cutMOSFET for measures against subthreshold leak) results in measuresagainst the at-standby current reduction, which are effective inreducing the off current. On the other hand, since the off current islittle produced in a lower temperature region, particularly in thevicinity of daily-used normal temperatures, the occupied rate of refreshcurrent increases. However, such a conventional DRAM as described abovedoes no disclose means effective in reducing the refresh current.

In a DRAM having complete compatibility with an SRAM, and a DRAM calleda pseudo SRAM in the above DRAMs, refresh operations are respectivelyalways performed by internal timers. Since these memories perform therefresh operations at all times even if they are at standby, theanalysis of AC and DC current components of at-standby currents in cutand divided states becomes difficult. Since only a refresh operatingcurrent based on a cycle always determined by the internal timer isevaluated, this will do harm even to an analysis made with a view towardexecuting lower current consumption with the extension of a refreshcycle. Further, a problem arises in that since a refresh operation isautomatically performed by an internal timer even upon evaluation of adata retention characteristic, a true data retention characteristiccannot be obtained.

An object of the present invention is to provide a semiconductor memorycircuit capable of reducing current consumption at non-operation in asystem equipped with a plurality of chips that share the use of a powersupply, address signals and a data bus. Another object of the presentinvention is to provide a semiconductor memory circuit such as a DRAM orthe like which has reduced an at-standby current by a reduction inrefresh operating current in a lower temperature region, particularly inthe neighborhood of daily-used normal temperatures. A further object ofthe present invention is to provide a semiconductor memory circuit suchas a DRAM or the like capable of performing more accurate characteristicevaluation. The above, other objects and novel features of the presentinvention will become apparent from the description of the presentspecification and the accompanying drawings.

A summary of a typical one of the inventions disclosed in the presentapplication will be described in brief as follows: In a memory circuit,switch means are respectively provided between VDD or VSS and a powersupply circuit. The switch means are controlled by an internal signalproduced from an external signal to cut current consumption of the powersupply circuit at deactivation or non-operation of the memory circuit.The supply of internal voltages to their corresponding internalcircuits, which are generated from the power supply circuit, is alsostopped and hence leak currents thereat are also cut.

When the current consumption is cut, an output terminal of an outputcircuit is brought to high impedance to ensure the operations of othercircuits on a system. In the memory circuit having a refresh timer, therefresh timer is also deactivated to stop a refresh operation.

In the memory circuit which performs a refresh operation, a dataretention characteristic has temperature dependence. By paying attentionto the fact that a characteristic in a low temperature region isenhanced, the internal refresh timer for data retention is caused tohave temperature dependence and provided with a signal for forcedlystopping an internal refresh operation signal. Further, it is caused tohave a function capable of externally controlling timing for the refreshoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one embodiment of a DRAM according tothe present invention;

FIG. 2 is a characteristic diagram depicting one embodiment illustrativeof internal voltages of a power supply circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing one embodiment of an input circuit11 shown in FIG. 1;

FIG. 4 is a circuit diagram illustrating one embodiment of an outputcontrol circuit 18 a shown in FIG. 1;

FIG. 5 is a circuit diagram showing one embodiment of an output circuit19 shown in FIG. 1;

FIG. 6 is an operation waveform diagram for describing one example ofthe operation of the DRAM shown in FIG. 1;

FIG. 7 is an operation waveform diagram for describing one exampleillustrative of operations of the output control circuit shown in FIG. 4and the output circuit shown in FIG. 5;

FIG. 8 is a block diagram illustrating another embodiment of a DRAMaccording to the present invention;

FIG. 9 is a characteristic diagram showing one embodiment of an internalvoltage of a power supply circuit shown in FIG. 8;

FIG. 10 is a circuit diagram showing one embodiment of an output controlcircuit 18 b shown in FIG. 8;

FIG. 11 is an operation waveform diagram for describing one example ofthe operation of the output control circuit 18 b shown in FIG. 10;

FIG. 12 is a block diagram showing a further embodiment of a DRAMaccording to the present invention;

FIG. 13 is a circuit diagram illustrating one embodiment of an inputcircuit 12 c shown in FIG. 12;

FIG. 14 is an operation waveform diagram for describing one example ofthe operation of the input circuit 12 c shown in FIG. 13;

FIG. 15 is a circuit diagram showing another embodiment of the inputcircuit 12 c shown in FIG. 12;

FIG. 16 is a block diagram illustrating one embodiment of a power supplycircuit shown in FIG. 12;

FIG. 17 is a circuit diagram depicting one embodiment of a referencevoltage circuit shown in FIG. 16;

FIG. 18 is a circuit diagram showing one embodiment of a step-downcircuit shown in FIG. 16;

FIG. 19 is a circuit diagram illustrating another embodiment of thestep-down circuit shown in FIG. 16;

FIG. 20 is a circuit diagram depicting one embodiment of a voltagesensor shown in FIG. 16;

FIG. 21 is an operation waveform diagram for describing one example ofthe operation of the voltage sensor shown in FIG. 20;

FIG. 22 is a circuit diagram showing one embodiment of a VPP pumpcircuit 77 shown in FIG. 16;

FIG. 23 is a circuit diagram illustrating one embodiment of anoscillator circuit 160 shown in FIG. 22;

FIG. 24 is an operation waveform diagram for describing one example ofthe operation of the pump circuit shown in FIG. 22;

FIG. 25 is an explanatory view showing one example illustrative of abreakdown of current consumption of a DRAM chip to which the presentinvention is applied;

FIG. 26 is a block diagram illustrating one embodiment of a systemincluding a memory chip according to the present invention;

FIG. 27 is an operation waveform diagram for describing one example ofthe operation of the embodiment shown in FIG. 26;

FIG. 28 is a configurational diagram showing one embodiment of asemiconductor integrated circuit device according to the presentinvention;

FIG. 29 is a block diagram illustrating one embodiment of a refreshtimer mounted in a DRAM according to the present invention;

FIG. 30 is a circuit diagram showing one embodiment illustrative of acurrent source 200 and a level converting current source 201 shown inFIG. 29;

FIG. 31 is a circuit diagram depicting one embodiment of a ringoscillator 202 shown in FIG. 29;

FIG. 32 is a characteristic diagram for describing temperaturedependence of the refresh timer according to the present invention;

FIG. 33 is a block diagram showing another embodiment of a refresh timermounted in a DRAM according to the present invention;

FIG. 34 is a circuit diagram depicting one embodiment illustrative ofcurrent sources 200, 242 and 243 shown in FIG. 33;

FIG. 35 is a characteristic diagram for describing temperaturedependence of each current source shown in FIG. 34;

FIG. 36 is a characteristic diagram for describing temperaturedependence of the refresh timer shown in FIG. 33;

FIG. 37 is a circuit diagram showing another embodiment illustrative ofthe current sources 200, 242 and 243 shown in FIG. 33;

FIG. 38 is a circuit diagram showing a further embodiment illustrativeof the current sources 200, 242 and 243 shown in FIG. 33;

FIG. 39 is a block diagram illustrating a further embodiment of arefresh timer mounted in a DRAM according to the present invention;

FIG. 40 is a characteristic diagram for describing a refresh operationcarried out by the refresh timer shown in FIG. 39;

FIG. 41 is a waveform diagram for describing one example of theoperation of the refresh timer shown in FIG. 39;

FIG. 42 is a waveform diagram for describing another example of theoperation of the refresh timer shown in FIG. 39;

FIG. 43 is a logic circuit diagram showing one embodiment illustrativeof an operation determination circuit 283 and a control circuit 284shown in FIG. 39; and

FIG. 44 is a block diagram showing a still further embodiment of arefresh timer according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

A block diagram of one embodiment of a DRAM according to the presentinvention is shown in FIG. 1. Respective circuit blocks that constitutea memory chip 10 a according to this embodiment, are formed on a singlesemiconductor substrate like monocrystalline silicon by the known MOSintegrated circuit manufacturing technology. Although not restricted inparticular, the DRAM according to the present embodiment has aninput/output interface corresponding to a static RAM to enablereplacement with the static RAM.

In the present embodiment, a source or power supply voltage VDD suppliedfrom an external terminal is used as an internal power supply voltageVDDIN via switch means 20 a and supplied to an input circuit 12 and apower supply circuit 13 a as an operating voltage. Although notrestricted in particular, the switch means 20 a is controlled based on apower-down signal PD produced from a control signal CS2 corresponding toa signal for giving instructions for a deep power-down mode (hereinaftercalled simply “DPD”) in the static RAM. Namely, the signal CS2 inputtedfrom the external terminal is inputted to the input circuit 11 broughtinto an operating state on a steady basis by the power supply voltageVDD supplied from the external terminal, after which the power-downsignal PD is generated via the input circuit 11.

An internal voltage VPERI formed or produced by the power supply circuit13 a is supplied to a control circuit 15 and a read circuit 17, whereasa boost voltage VPP and a step-down voltage VDL are supplied to a memoryarray 16. An output MO of the read circuit 17 operated based on theinternal voltage VPERI, and an output control signal DOEP formed by thecontrol circuit 15 are inputted to an output circuit 19 via an outputcontrol circuit 18 a. The output control circuit 18 a is also controlledby the power-down signal PD.

The input circuit 11 is brought into the operating state on the steadybasis by the power supply voltage VDD supplied from the externalterminal as described above, whereas the read circuit 17 and the controlcircuit 15 are operated by the internal voltage VPERI generated by thepower supply circuit 13 a. The internal voltage VPERI is shut off orinterrupted by an operation stop of the power supply circuit 13 a, whichcorresponds to an off state of the switch means 20 a. The output controlcircuit 18 is operated on a steady basis by the power supply voltage VDDsupplied from the external terminal and prevents the operation of theoutput circuit 19 from being instabilized by undefined levels of thesignals DOEP and MO respectively formed by the control circuit 15 andthe read circuit 17 at which the power-off is done by the signal PD.

In the present embodiment, a timer 14 for refresh is also controlled bythe power-down signal PD to reduce current consumption in the above DPD,thereby stopping a refresh operation in the deep power-down mode.Namely, since the respective operating voltages VPERI, VPP, VDL of thecontrol circuit 15, read circuit 17 and memory array 16 are shut off,the refresh timer 14 is also deactivated because it is useless tooperate it.

In the DRAM according to the present embodiment, the memory array 16includes a plurality of memory cells which are provided in associationwith a plurality of bit lines BL and a plurality of word lines WL andeach of which needs a refresh operation for periodically holding memoryinformation. Each of the memory cells comprises an information storagecapacitor and an address selection MOSFET, for example. The gate of theaddress selection MOSFET is connected to its corresponding word line.One of source and drain paths is connected to its corresponding bitline, whereas the other thereof is connected to its correspondingstorage node of the storage capacitor.

The bit lines are provided in pair and connected to their correspondinginput/output nodes of sense amplifiers SA each comprising a differentiallatch circuit. Each of the memory cells is connected to one of each bitline pair according to a word line selecting operation, and no memorycell is connected to the other thereof. The sense amplifier carries outrewriting (or refresh operation) of regarding a precharge voltage on thebit line to which no memory cell is connected, as a reference voltage,amplifying a small potential difference between the precharge voltageand a read signal read into the bit line to which each memory cell isconnected, to a high level and a low level, and restoring the state ofan electrical charge of each storage capacitor, which is likely to loseaccording to the word line selecting operation, to its original storagestate. Such a configuration can make use of one identical to one for thedynamic RAM known to date.

The memory array 16 is provided with a word driver WD for selecting eachword line WL and a column selection circuit for selecting each bit lineBL. The boost voltage VPP is supplied to the word driver WD to increasethe level of selecting the word line WL. The step-down voltage VDL isset as an operating voltage for the sense amplifier SA to define a highlevel stored in each memory cell. A differential voltage between the VDLand VPP is set so as to be identical to or slightly higher than aneffective threshold voltage between the gate and source of the addressselection MOSFET and enables full writing to the correspondingcapacitor.

The input circuit 12 is an input circuit for receiving an address signalAi and a chip select signal CS1B therein and supplies the input signalC1B and address signal ABi to the control circuit 15. Although notrestricted in particular, the control circuit 15 includes an addresstransition detection circuit and generates timing signals or the likefor row-system control and a column system.

In each of the dynamic memory cells referred to above, informationcharge stored in the corresponding capacitor will be lost with theelapse of time. Therefore, the dynamic memory cell needs the refreshoperation of performing a read operation before such information chargeis lost and restoring its state to the original state of charge. Thetimer 14 forms a predetermined time signal corresponding to informationholding capacity of the memory cell. A signal RF outputted from thetimer 14 is inputted to the control circuit 15 and used to executerefresh for an address specified by a refresh address counter.

In the DRAM of the present embodiment, although not restricted inparticular, the control circuit 15 performs control for detecting thetransition of an external row address signal, i.e., early one of asignal outputted from its row address transition detection circuit and asignal RF outputted from its internal refresh timer, executing either anormal memory access or a refresh operation and executing thenon-executed operation after its execution. Thus, since there is nomalfunction even if the internal refresh operation and the externalaccess collide with each other, an external refresh request can be madeunnecessary.

A characteristic diagram of one embodiment illustrative of internalvoltages outputted from the power supply circuit shown in FIG. 1 isshown in FIG. 2. With respect to the internal voltage VDDINcorresponding to the power supply voltage VDD supplied from the externalterminal, the internal step-down voltage VDL is stepped down to aconstant voltage of 1.8V, and the internal voltage VPERI for theperipheral circuit is stepped down to a constant of 2.3V. The boostvoltage VPP is boosted to 3.6V. Although not restricted in particular,the boost voltage VPP is stabilized by supplying the VPERI or VDL to acharge pump circuit and forming it thereat.

A circuit diagram of one embodiment of the input circuit 11 shown inFIG. 1 is shown in FIG. 3. The input circuit is used to receive a CS2signal and comprises three-stage CMOS inverter circuits 26, 27 and 28respectively brought to an operating state by the power supply voltageVDD supplied from the external terminal and a circuit 's groundpotential VSS. Since such operating voltages VDD and VSS are supplied ona steady basis, the input circuit is always operable and forms apower-down signal PD corresponding to a change in the signal CS2. In thepresent embodiment, the power-down signal PD is brought to an invertedsignal of the external signal (chip select signal) CS2 by the threeinverter circuits 26 through 28. However, the power-down signal PD isnot limited to it. Such a signal as to be controlled by the externalsignal and turn off the switch means 20 a in a DPD mode may be used.

A circuit diagram of one embodiment of the output control circuit 18 ashown in FIG. 1 is shown in FIG. 4. Since each of input signals MO andDOEP inputted to the output control circuit 18 a has signal amplitudecorresponding to the above-described internal voltage VPERI, whereas anoperating voltage of the output circuit 19 is given as the power supplyvoltage VDD as described above, a level converting circuit 30 isprovided. The level converting circuit 30 converts signals MO and DOEPeach having a VPERI level to signals CO and DOE each having a VDD level.A level conversion section corresponding to the input signal DOEPcomprises P channel MOSFETs 31 and 33 provided in a latch form, an Nchannel MOSFET 32 provided between the drain of the MOSFET 31 and theinput signal DOEP and having a gate to which VPERI is applied, and an Nchannel MOSFET 34 that receives the input signal DOEP therein. The levelconverting circuit 30 corresponding to the input signal MO is alsosimilar to the above.

An inverter circuit 39 operated by the power supply voltage VDD forms aPDB signal obtained by inverting the power-down signal PD and controlsan N channel MOSFET 35 and a P channel MOSFET 36 added to the levelconversion section. Namely, the MOSFET 35 and the MOSFET 36 arerespectively turned off and turned on in response to a low level of thesignal PDB. Thus, an internal node NO is fixed to a high level withoutdepending on the input signal DOEP, and DOE is fixed to a low level.Further, an output DQ of a chip is brought to high impedance. In the DPDmode referred to above, a DC current is cut off by the off-state of theMOSFET 35 so that the level converting circuit 30 is brought to lowconsumption power.

A circuit diagram of one embodiment of the output circuit 19 shown inFIG. 1 is shown in FIG. 5. In the output circuit employed in the presentembodiment, NAND gate circuits 42 and 43 and an inverter circuit 44controlled by the output control signal DOE control a P channel outputMOSFET 40 and an N channel output MOSFET 41. A data signal CO and aninverted signal formed by the inverter circuit 45 are respectivelysupplied to the other inputs of the gate circuits 43 and 42. When theoutput control signal DOE is low in level, a drive signal DQP is broughtto a high level and a drive signal DQN is brought to a low level. Thus,the output MOSFETs 40 and 41 are both brought to an off state regardlessof the level of the data signal CO so that the output DQ is brought tohigh impedance. When the data signal CO is set as a pair of differentialsignals by the output control circuit 18 a, the inverter circuit 15becomes unnecessary and a bar signal (inverted signal) may be inputtedto the NAND gate circuit 42.

An operation waveform diagram for describing one example of theoperation of the DRAM shown in FIG. 1 is shown in FIG. 6. A DRAM chip 10a has four types of states of power off, DPD (deep power-down), standby,and an operation according to the power supply voltage VDD and signalsCS2 and CS1B.

When the signal CS is low in level in a state in which the power supplyvoltage VDD is applied, the DRAM is brought to a DPD mode 22. At thistime, the power-down signal PD results in a high level and the switchmeans 20 a is turned off so that VDDIN is brought to a low level (0V).Thus, the input circuit 12 and the power supply circuit 13 a arepower-off so that their circuit operations are stopped. With suchdeactivation of the power supply circuit 13 a, all of the internal powersupply voltages VPERI, VPP and VDL are brought to the low level (0V).Consequently, each of the power supply circuit 13 a, input circuit 12,control circuit 15, memory array 16 and read circuit 17 assumes acurrent consumption of 0. The timer 14 is also deactivated by the PDsignal and hence a refresh operating current also results in 0. Further,the activation signal DOE for the output circuit becomes low in level bythe PD signal in the output control circuit 18 a, so that the output DQis brought to high impedance.

When the CS2 is taken high in level in the state in which the powersupply voltage VDD is applied, the DRAM is brought to a standby state23. The power-down signal PD becomes low in level and the switch means20 a is turned on so that the internal power supply voltage VDDIN isbrought to a high level. Thus, the power supply circuit 13 a is broughtto an operating state to generate predetermined voltages VPERI, VPP andVDL. Incidentally, the timer 14 is operated during this standby periodto output an RF signal for each predetermined period 25, whereby arefresh operation is performed so as to hold data for the memory array16.

When the CS2 is taken high in level and the CSLB is taken low in levelin the state in which the power supply voltage VDD is applied, the DRAMis brought to an on-operation 24 so that the corresponding memory array16 is selected according to the external address signal Ai, whereby datais read as MO. Based on the control signal DOEP, the output circuit isactivated to output DQ. Since the external power supply voltage VDD perse is shut off in a power-off state 21, all the circuits aredeactivated.

An operation waveform diagram for describing one example illustrative ofthe output control circuit shown in FIG. 4 and the output circuit shownin FIG. 5 is shown in FIG. 7. At standby, DOE is low in level and anoutput DQ is brought to high impedance. Upon operation, DOE becomes highin level according to DOEP, and the output DQ is outputted according toread data signals MO and CO. Upon DPD, a PD signal is brought to a highlevel, and DOE is taken low in level regardless of DOEP and MO even ifinternal power supply voltages are stopped and DOEP and MO are takenundefined. Thus, the output DQ is brought to the high impedance.

A block diagram of another embodiment of a DRAM according to the presentinvention is shown in FIG. 8. In the present embodiment, VDD is indentedfor a case in which it is used as low as about 2.5V. Therefore, thepresent embodiment is different from the embodiment shown in FIG. 1 inthat an operating voltage supplied to each peripheral circuit is set soas to be equal to VDD. Therefore, switch means 20 b is added to acontrol circuit 15 and a read circuit 17, and a power supply voltage VDDsupplied from outside via such switch means 20 b is supplied to therespective circuits 15 and 17 as an internal voltage VPERI.

In response to the above setting of the operating voltage, a powersupply circuit 13 b generates only an internal step-down voltage VDL anda boost voltage VPP. Since VPERI is set to a low level upon DPD toreduce a leak current even in the case of this embodiment, the switchmeans 20 b is necessary. Thus, the switches 20 a and 20 b are controlledin the same manner as described above according to a power-down signalPD formed by their corresponding input circuit 11. The presentembodiment is identical in other configuration to the embodiment shownin FIG. 1 as well as in operation and is capable of obtaining similareffects.

A characteristic diagram of one embodiment illustrative of internalvoltages produced from the power supply circuit shown in FIG. 8 is shownin FIG. 9. The reference label VDDIN indicates an internal voltage, andthe reference label VPERI indicates an internal voltage. In the presentembodiment, VPERI=VDD. VDL and VPP are similar to those shown in FIG. 8.Namely, the operating voltage VPERI for each peripheral circuit is setto the same in association with the power supply voltage VDD suppliedfrom an external terminal, an internal step-down voltage VDL is boostedto 1.8V, and a boost voltage VPP is boosted to 3.6V.

A circuit diagram of one embodiment of an output control circuit 18 bshown in FIG. 8 is shown in FIG. 10. Since VPERI=VDD upon standby andoperation in the present embodiment, level conversion becomesunnecessary. Thus, the level converting function shown in FIG. 4 isomitted and a logic circuit 50 forms a buffer circuit in which a Pchannel MOSFET 51 and an N channel MOSFET 52 receive a signal DOEP. An Nchannel MOSFET 53 and a P channel MOSFET 54 controlled by a signal PDBare provided in a manner similar to the circuit shown in FIG. 4. Namely,the logic circuit constitutes a NAND gate circuit comprising the MOSFETs51, 52, 53 and 54 and is supplied with the signals DOEP and PD. A signaloutputted therefrom is outputted as a signal DOE via an inverter circuitwhich comprises MOSFETs 55 and 56. A logic circuit 50 corresponding toan input signal MO is similar to the above.

An operation waveform diagram for describing one example of theoperation of the output control circuit 18 b shown in FIG. 10 is shownin FIG. 11. At standby 23, the DOEP signal generated by the controlcircuit 15 is low in level and DOE is brought to a low level, and achip's output DQ is brought to high impedance. Upon an operation 24, theoutput control circuit 18 b outputs a data signal CO according to anoutput MO from the read circuit 17. DOEP is also brought to a high levelso that DOE is taken high in level. Thus, an output circuit 19 isactivated.

Upon DPD 22, the PD signal becomes high in level and a PDB signalbecomes low in level. Therefore, DOE is forcedly fixed to a low leveland the chip's output DQ is brought to high impedance. Since the supplyof the voltage for VPERI is cut upon DPD, MO and DOEP operated withVPERI become undefined. However, since PDB is set to the low level, theoutputs CO and DOE are respectively fixed to the low level. Since the Nchannel MOSFET 53 is turned off, no through current does not floweither.

In the embodiment shown in FIG. 1, a large current flows because theswitch means 20 a supplies the voltage VDDIN and the current to theinput circuit 12 and the power supply circuit 13 a. With a view towardreducing a voltage drop developed due to the parasitic resistance of theswitch means 20 a, it is necessary to appreciably increase the constantof MOSFET constituting the switch means 20 a. However, it is alsoconsidered that since a problem about an increase in layout area arises,a VDDIN wiring is added within the chip, and the parasitic resistance ofeach wiring is also reduced, a thick wiring of about several tens of μm,for example is required and hence the layout area further increases.

A block diagram of a further embodiment of a DRAM according to thepresent invention is shown in FIG. 12. In the present embodiment, aninput circuit 12 c and a power supply circuit 13 c respectively carryout such a contrivance as to separately perform current cut upon DPD inconsideration of the above problem in the embodiment shown in FIG. 1.Namely, a power supply voltage VDD supplied from an external terminal issupplied to the input circuit 12 c and the power supply circuit 13 c ona steady basis respectively. A signal PD is supplied to the inputcircuit 12 c and the power supply circuit 13 c to carry out current cutupon DPD individually. In addition to the above, the present embodimentis similar to and identical to the FIG. 1 in operation too.

In the present embodiment, a wiring for an internal power supply voltageVDDIN becomes unnecessary and a layout area can be reduced. In the powersupply circuit 13 c, as will be described later, a voltage applied tothe gate of an output MOSFET for supplying each voltage and current iscontrolled so that the current is cut upon DPD. Thus, the MOSFET largein current supply capacity like the switch means 20 a shown in FIG. 1becomes unnecessary. The power supply circuit can comprise only a smallcircuit for controlling the gate voltage of the output MOSFET, and thelayout area can be reduced.

A circuit diagram of one embodiment of the input circuit 12 c shown inFIG. 12 is shown in FIG. 13. The input circuit 12 c comprises aplurality of logic circuits 65 corresponding to external input signals.As a logic circuit 65 corresponding to an external input signal CS1B isillustratively shown as typical, the logic circuit 65 comprises a NORgate circuit made up of MOSFETs 66, 67, 68 and 69, and an invertercircuit made up of MOSFETs 70 and 71. The logic circuit 65 is operatedwith a source voltage VDD supplied from an external terminal.

The respective logic circuits 65 corresponding other signals A0 throughAi including the signal CS1B are commonly supplied with a power-downsignal PD as a control signal. The present embodiment shows a case inwhich external input signals (chip select signal CS1B and address signalAi) and their output signals (C1B and ABi) are in phase. However, aninverter circuit may be added to the logic circuit 65 according to thenext-stage circuit receiving the output signals therein so that they areset as inverted signals.

An operation waveform diagram for describing one example of theoperation of the input circuit 12 c shown in FIG. 13 is shown in FIG.14. Upon standby 23 and an operation 24, the power-down signal PD isbrought to a low level in response to a high level of a signal CS2, andC1B and ABi are outputted according to the external input signals (chipselect signal CS1B and address signal Ai), so that the next-stageinternal circuits are operated.

Upon DPD 22 corresponding to a low level of the signal CS2, thepower-down signal PD is brought to a high level and the MOSFET 66 ofeach logic circuit 65 is turned off and the MOSFET 69 is turned on.Thus, an internal node N2 is fixed to a low level and the outputs (C1Band ABi) are respectively fixed to a high level. Since the outputs (C1Band ABi) remain unchanged even if the external input signals aretransitioned, current consumption will result in 0. Since the P channelMOSFET 66 of each logic circuit 65 is turned off, no through currentflows even if the corresponding external input signal is given as anintermediate potential.

A circuit diagram of another embodiment of the input circuit 12 c shownin FIG. 12 is shown in FIG. 15. The input circuit 12 c employed in thepresent embodiment is different from the embodiment shown in FIG. 13 inthat an output C1B of a chip select signal CS1B other than a power-downsignal PD is inputted to respective logic circuits 65 which receiveaddress signals A0 through Ai. Upon standby, the chip select signal CS1Bis brought to a high level and the output C1B is also taken high inlevel. Thus, the respective logic circuits 65 that receive the addresssignals A0 through Ai, are respectively fixed to a high level in amanner similar to upon DPD in the embodiment of FIG. 13 and capable ofreducing at-standby current consumption. This configuration is capableof performing sharing of a load on the input circuit 11 for forming thepower-down signal PD.

While the embodiments shown in FIGS. 13 and 15 are ones wherein thedescription of the input circuits 12 c has been made using the addresssignals Ai, other external input signals (write control signal, datainput signal, etc.) may be applied similarly according to the memorychip. However, the input circuit 11 for receiving CS2 for controllingDPD is not included.

While signal paths for inputting write data are omitted in therespective embodiments shown in FIGS. 1, 8 and 12, it should beunderstood that a data input circuit is included in the output circuit19 and a write amplifier is included in the read circuit 17. While theterminal DQ is used for both the output and input of data, the datainput terminal may be provided discretely as needed.

A block diagram of one embodiment of the power supply circuit shown inFIG. 12 is shown in FIG. 16. The present embodiment comprises areference voltage circuit 73, step-down circuits 74 and 75, a voltagesensor 76, a pump circuit 77 and switch means 78. The respectivecircuits 73 through 77 are controlled by a PD signal and a PDB signalinverted by an inverter circuit 879.

In the reference voltage circuit 73, step-down circuits 74 and 75 andvoltage sensor 76, switch means (80 through 87) are respectivelyprovided between VDD and VSS in their circuits. The switch means 80through 87 are switch-controlled by the PDB signal formed by theinverter circuit 79. Upon DPD, the respective switch means 80 through 87are turned off to cut the supply of a voltage and a current to thecircuits 73 through 77. Thus, the current consumed by each of thecircuits 73 through 77 results in 0. Since VPERI and VDL used as outputvoltages are discharged to OV because the voltage supply is stopped. Thepump circuit 77 stops its pump operation according to the PD signal tobring current consumption to 0. Upon DPD, the switch means 78 is turnedoff and the voltage supply is stopped, so that a boost voltage VPP isalso discharged to 0V.

As described above, the currents consumed by all the power supplycircuits that respectively constitute the power supply circuits, resultin 0. With the deactivation of these power supply circuits, the voltagesupply is stopped so that the internal voltages VPERI, VDL and VPP arealso brought to 0V. Therefore, current consumption results in 0 even inthe case of the circuits (the control circuit 15, memory array 16 andread circuit 17 shown in FIG. 12) operated with these internal voltagesVPERI, VDL and VPP.

A circuit diagram of one embodiment of the reference voltage circuitshown in FIG. 16 is shown in FIG. 17. The reference voltage circuitcomprises a reference voltage generating circuit and a reference voltagelevel converting circuit. The reference voltage generating circuitextracts or takes out a difference voltage between a base and anemitter, corresponding to the difference in emitter current densitybetween bipolar transistors 97 and 98, causes it to flow through aresistor 94 to thereby form a constant current, and allows the constantcurrent to flow through a resistor 101 by virtue of a current mirrorcircuit to thereby form a reference voltage VREF. The resistor 101 issupplied with a base-to-emitter voltage VBE of a transistor 102 to carryout temperature compensation.

The reference voltage level converting circuit compares the referencevoltage VREF and a voltage at a node N10, which is formed by causing acurrent I0 to flow through series resistors 110 through 113, by means ofdifferential MOSFETs 105 and 106, and forms such a control voltage VPGthat both coincide with each other to thereby control a MOSFET 109 forforming the current I0. With the operation of the differential circuit,the reference voltage VREF and the potential at the node N10 coincidewith each other, and it is divided by the series resistor circuit of 110through 113 to form level-converted reference voltages VR1, VR2 andVRTR.

N channel MOSFETs corresponding to MOSFETs 95 and 96 added to performcurrent cut at DPD, and P channel MOSFETs designated at numerals 99, 108and 114 are added. An N channel MOSFET designated at numeral 107 is anelement for forming an operating current for a differential amplifier,which is used for the current cut at DPD by being controlled based on aPDB signal.

The description at standby and operation of the reference voltagecircuit employed in the present embodiment is as follows. VREF becomes aconstant voltage which does not depend on the temperature and VDD. Thereference voltage level converting circuit controls VPG so that VREF andthe internal node N10 take the same voltage. The current I0 flowsthrough the P channel MOSFET 109. The voltage at the internal node N10is determined based on the current I0 and the resistors 110, 111, 112 an113. The current I0 becomes a constant current which does not depends onthe temperature and VDD. The respective output voltages VR1, VR2 andVRTR are determined by the current I0 and the resistors 110, 111, 112and 113 and result in constant voltages which does not depend on thetemperature and VDD.

Upon DPD, PDB becomes a low level and the MOSFETs 95, 96 and 107 areturned off to cut a current path to the VSS side. On the other hand, theP channel MOSFET 99 is turned on to increase a node N3 to the powersupply voltage VDD. Thus, P channel MOSFETs 90, 91 and 100 in which N3is used as their gate inputs, are turned off to cut a current from thepower supply voltage VDD. Similarly, the P channel MOSFETs 108 and 114are turned on to raise a node N8 and VPG to VDD. Consequently, theircorresponding P channel MOSFETs 103, 104 and 109 are turned off to cutthe current from the power supply voltage VDD. Since the currents fromVDD and VSS are cut in this way, current consumption results in 0.

The respective output voltages VR1, VR2 and VRTR are discharged to 0Vthrough the resistors 110, 111, 112 and 113. Since the MOSFETs 95 and 96switch-controlled by the PDB signal are added to provide speeding up andstabilization of the operation, they may be omitted.

A circuit diagram of one embodiment of the step-down circuit shown inFIG. 16 is shown in FIG. 18. The present embodiment is a circuit forgenerating a voltage VPERI equal to twice the reference voltage VR1. Thepresent circuit comprises a differential amplifier section includingMOSFETs 117 and 118, and an output section including a MOSFET 122.Namely, P channel MOSFETs 123 and 124 provided in a diode form areprovided between the drain of the output MOSFET 122 and a circuit'sground potential and supplied with a current from the output MOSFET 122.A differential amplifier is operated so as to allow a voltage at a nodeN13 corresponding to a connecting point of both the MOSFETs 123 and 124and the reference voltage VR1 to coincide with each other, whereby avoltage formed by a series circuit of the two diode-configured MOSFETs123 and 124 is set to the voltage VPERI equal to twice the referencevoltage VR1.

P channel MOSFETs 120 and 121 for current cut are added in the presentembodiment. A MOSFET 119 is one for forming an operating current of thedifferential amplifier. The MOSFET 119 is one used for supplying a PDBsignal thereto to thereby cut an operating current at DPD.

Upon standby and operation, the MOSFETs 123 and 124 form the voltageequal to one half of VPERI at the node N13 as described above. Thedifferential amplifier section compares VR1 and the voltage at the nodeN13. When VR1>N13, the potential. at a node N11 is lowered so that the Pchannel MOSFET 122 increases the supply of a current to the MOSFETs 123and 124. When VR1<N13 in reverse, the potential at the node N11 israised so that the P channel MOSFET 122 reduces the supply of thecurrent to the MOSFETs 123 and 124. The present embodiment controls soas to bring about VR1=N13 and serves so as to hold VPERI as a constantvoltage.

Upon DPD, the PDB signal is taken low in level and the MOSFET 119 isturned off to cut a current to the VSS side. On the other hand, the Pchannel MOSFETs 120 and 121 are turned on to raise the nodes N11 and N12to VDD. Consequently, their corresponding P channel MOSFETs 115, 116 and122 are turned off so that the current from VDD is also cut. Owing tothe above, current consumption at DPD can be brought to 0.

The P channel MOSFET 122 for supplying a current for the step-downvoltage VPERI needs large drive capacity, and its layout area is alsolarge. When the switch means 20 a is made up of the P channel MOSFET andis inserted between the P channel MOSFET and VDD as in the embodimentshown in FIG. 1, the respective P channel MOSFETs need a size equal totwice that shown in FIG. 18 and is increased to four times in layoutarea. On the other hand, since the P channel MOSFET 121 for increasingthe potential at the node N11 inputted to the gate of the MOSFET 122, toVDD may be low in drive capacity in the case of the configuration shownin FIG. 18, its layout area can be reduced.

A circuit diagram of another embodiment of the step-down circuit shownin FIG. 16 is shown in FIG. 19. The present embodiment is a step-downcircuit for generating a voltage VDL equal to twice the referencevoltage VR2. The present embodiment is different from the embodiment ofFIG. 18 in that a differential amplifier section is provided as atwo-stage configuration and the amplitude at an output node N17 of adifferential amplifier is increased. The present embodiment is similarto FIG. 18 in other points. Increasing the amplitude at the output nodeN17 of the differential amplifier makes it possible to reduce atransistor size of an output P channel MOSFET 141. Namely, since agate-to-source voltage Vgs can be made great, a large current can becarried even if the transistor size is reduced. For the purpose ofon-DPD, P channel MOSFETs 138, 139 and 140 for current cut are added.The subsequent configuration is similar to the embodiment shown in FIG.18.

A circuit diagram of one embodiment of the voltage sensor shown in FIG.16 is shown in FIG. 20. The voltage sensor of the present embodiment isone wherein when the voltage of VPP is lower than a constant voltage,the reduction or drop in the voltage is detected to bring VPS to a highlevel, and a pump circuit is activated to increase the voltage of VPP.The voltage sensor comprises a reference voltage section, a differentialamplifier section and an output section. P channel MOSFETs 145, 146 and147 set in a diode form are provided to divide VPP and form a dividedvoltage of (VPP−VDL)/2 from an output node N20. Differential MOSFETs 151and 152 compare the voltage at the node N20 and a reference voltage VR2and outputs a detect signal VPS from an inverter circuit 155 accordingto the result of comparison. While the differential amplifier sectionhas been described as a one-stage configuration in the presentembodiment, the differential amplifier having the two-stageconfiguration, which is used in FIG. 19, may be adopted.

P channel MOSFETs 148 and 154 are added for current cut at DPD. An Nchannel MOSFET 153 is a constituent element of the differentialamplifier in the same manner as described above. This is also one usedfor supplying a PDB signal to the gate of the MOSFET 153 and therebyperforming current cut of the differential amplifier at DPD.

An operation waveform diagram for describing one example of theoperation of the voltage sensor shown in FIG. 20 is shown in FIG. 21.When a circuit (word driver WD of memory array 16 shown in FIG. 12)supplied with the boost voltage VPP is operated, VPP becomes low. Thus,when the voltage at N20 is lowered and N20<VR2(=0.9V), N21 becomes lowin level, and the output VPS is brought to a high level. At this time,the pump circuit of VPP is operated to increase VPP. When VPP isincreased by the operation or the like of the pump circuit at thenon-selection of a word like and thereby the voltage at N20 is raisedand N20>VR2 (=0.9V), N21 is taken high in level and the output VPSbecomes low in level. Thus, the pump circuit of VPP is deactivated. Theoperation of the pump circuit is controlled by the output VPS of such avoltage sensor so that such a boost voltage VPP as regarded as constantcan be obtained.

Upon DPD, the PDB signal becomes low in level and hence the MOSFET 153is turned off to cut a current to VSS. On the other hand, the P channelMOSFETs 148 and 154 are turned on to raise the nodes N21 and N22 to VDD.Therefore, P channel MOSFETs 149 and 150 are turned off to cut a currentfrom VDD. Since the node N21 is fixed to VDD, the inverter circuit 155fixes the output VPS to the low level and causes no current to floweither.

One embodiment of a VPP pump circuit 77 shown in FIG. 16 is illustratedin FIG. 22. The pump circuit 77 comprises an oscillator circuit 160,boost capacitors 161, 162 and 163, a charge transfer N channel MOSFET167, and precharge N channel MOSFETs 164, 165 and 166. Although notrestricted in particular, an output voltage VPPH of the pump circuit issupplied to an internal voltage VPP via switch means 78. The switchmeans 78 comprises a P channel MOSFET 168 and is controlled by a PDsignal.

The boost voltage VPP is supplied to the word driver WD of the memoryarray 16 employed in the embodiment shown in FIG. 12. The output of theword driver WD is made up of a P channel MOSFET 170 and an N channelMOSFET 171. An output signal thereof is set to a level for selectingeach word line WL. While a main word line MWL takes VPP in a standbystate and the P channel MOSFET 170 is turned off, a small off-currentflows. Since the number of word lines WL increases like about 1600 inthe case of such a DRAM that its memory capacity is of 32 M bits, eventhe small off-current results in an innegligible current (several tensof .mu.A) over the whole chip. Therefore, the cutting of the supply ofthe current to VPP is meaningful upon DPD. The switch means 78 is madeup of the P channel MOSFET 168 as described above and controlled by thePD signal having VDD amplitude, whereby the supply of the current to VPPcan be fully cut.

A circuit diagram illustrating one embodiment of the oscillator circuit160 shown in FIG. 22 is shown in FIG. 23. The oscillator circuit 160comprises a ring oscillator which comprises a NAND gate circuit 172 andinverter circuits 173 through 176. The NAND gate circuit 172 and theinverter circuits 173 through 176 are operated by a step-down voltageVDL corresponding to a constant voltage to thereby hold an oscillationcycle or period constant. Namely, a problem arises in that when they areoperated by the power supply voltage VDD, the voltage changes withinspecs, when the oscillation period is excessively short, the efficiencyof conversion by the pump circuit is degraded, and when the oscillationperiod is excessively long, the supply capacity of a current isdegraded. In the present embodiment, a pulse having a desiredoscillation period or cycle can be stably obtained by operating theoscillator circuit with the constant voltage VDL.

Although not restricted in particular, the ring oscillator is controlledby the output signal VPS of the voltage sensor. When VPS is high inlevel, it oscillates, whereas when VPS is low in level, it isdeactivated. The operation of the pump circuit is controlled under thecontrol of such an oscillator circuit. Reference numeral 177 indicates alevel converting circuit. In the level converting circuit, an invertercircuit 186 forms complementary pulses N31 and N32 and supplies them tothe input of a CMOS inverter circuit which comprises N channel MOSFETs182 and 185 and P channel MOSFETs 181 and 184. Such P channel MOSFETs180 and 183 as to perform a latch operation in response to outputs ofother inverter circuits each other are provided between the drains ofthe P channel MOSFETs 180 and 183 and the power supply voltage VDD tothereby convert an output node N30 of the ring oscillator from a VDLlevel to a VDD level.

An N channel MOSFET 189 controlled by a PDB signal and a P channelMOSFET 179 are added. Upon DPD, the MOSFET 189 is turned off and theMOSFET 179 is turned on to fix an output signal OSC to a low level andfix OSCB to a high level.

An operation waveform diagram for describing one example of theoperation of the pump circuit shown in FIG. 22 is illustrated in FIG.24. When VPS is taken high in level upon standby and an operation, aninternal node N24 is boosted to 2VDD by OSC and an electrical charge istransferred to VPP via the MOSFETs 167 and 168.

Upon DPD, N24 and N25 are both fixed to VDD. The output VPPH of the pumpcircuit is simply lowered to VDD−Vth by the P channel MOSFET 168. Since,however, the gate PD of the P channel MOSFET 168 of the switch means 78is VDD, a gate voltage thereat becomes higher than a voltage at thesource thereof. Thus, the P channel MOSFET 168 is fully turned off sothat VPP is discharged to OV. Therefore, the off-current at the worddriver WD can be brought to 0.

In the normal DRAM, an information holding characteristic of each memorycell is enhanced with a substrate potential of a memory array as anegative voltage VBB lower than VSS. It should be understood that whilethe substrate voltage VBB is omitted in the respective embodiments shownin FIGS. 1, 8 and 12, a VBB generating circuit is included in each ofthe power supply circuits 13 a, 13 b and 13 c, and a VBB voltage issupplied to the memory array 16.

The VBB generating circuit has a configuration similar to the VPPgenerating circuit shown in FIG. 16 and comprises a voltage sensor and apump circuit. In the voltage sensor, switch means is provided betweenVDD and VSS and switch-controlled by a PDB signal to cut the supply of avoltage and a current upon DPD. The operation of the pump circuit iscontrolled by the PDB signal. Upon DPD, the pump circuit stops its pumpoperation to stop the supply of a current and a voltage to VBB. Thus,current consumption at DPD results in 0 even in the VBB generatingcircuit.

An explanatory view showing one example illustrative of a breakdown ofcurrent consumption of a DRAM chip to which the present invention isapplied, is shown in FIG. 25. Although not restricted in particular,memory capacity thereof is about 32 M bits, an interface hascompatibility with a static RAM, and a refresh operation is set as aso-called time multiplex system wherein the read/write operation and therefresh operation are executed by allocating their times thereto duringone cycle or the two operations are carried out only when the read/writeoperation and the refresh operation compete with each other.

The DRAM according to the present embodiment has a current consumptionof about 170 .mu.A at standby. The breakdown thereof is as follows.About 90 .mu.A is used as a refresh operating current, an off current(subthreshold leak current) of MOSFET is used as about 60 .mu.A, andabout 20 .mu.A is used as a DC current in the power supply circuit. Atstandby, i.e., when only the operation of holding data is performed, theDPD function or DPD mode like the present invention is provided for theDRAM having these current consumption to thereby bring the refreshoperation and the power supply circuit to a halt and bring each internalvoltage to 0, whereby the off current of the circuit operated by theinternal voltage can be brought to 0. Since it is necessary to cause theinput circuit 11 for receiving CS2 for giving instructions for recoveryfrom such a DPD mode, and other circuits on a system to coexist witheach other upon the above DPD, the output control circuit 18 a and theoutput circuit 19 are supplied with the power supply voltage VDD on astationary basis. Consequently, about 5 .mu.A corresponding to the offcurrent at MOSFET results in current consumption at above DPD in thecase of various switch means provided between such a power supply VDDand the respective circuits.

A block diagram of one embodiment of a system including a memory chipaccording to the present invention is illustrated in FIG. 26. In thepresent embodiment, a memory chip 10 a according to the presentinvention and another chip (ROM in the present embodiment) 190 arepackaged or mounted on the same substrate. Power supply lines like VDDand VSS, an address bus Ai, and a data bus DQ are provided on such amounting substrate. The two chips 10 a and 190 referred to above areconnected in common.

Control signal lines intended for the memory chip 10 a according to thepresent invention like CS2 and CS1B, and a control signal line intendedfor the ROM 190 like CEB are provided on the mounting substrate. Thededicated control signal lines are connected in association with theircorresponding memory chip 10 a and ROM 190.

A problem arises in that since a plurality of memory chips or the likeare mounted on such a system, a gate voltage of an output MOSFET in anoutput circuit, which is outputted to the data bus DQ, is brought to anundefined level when, for example, the supply of the power supplyvoltage VDD to the memory chip 10 a is shut off, and hence a currentformed based on a high level, which is outputted to the data bus, flowsinto the off-state output MOSFET of the memory chip 10 a according to aread signal from the ROM 190 or the like. Therefore, even in a state inwhich the memory chip 10 a is in a perfectly non-operated state, itneeds to take such measures as not to cause a current to flow in eachcircuit connected to a data bus, an address bus, a control bus, etc.

In the present embodiment, a DPD mode is specified according toinstructions given from a host system such as a CPU or the likeconnected to the bus during a predetermined period in which the memorychip 10 a does not perform any operation. Thus, the memory chip 10 asuch as the DRAM or the like is capable of realizing a so-calledultralow current consumption mode in which only the current of about 5.mu.A flows, without impairing the operations of other ROM 190 and thelike mounted on the same system.

An operation waveform diagram for describing one example of theoperation of the embodiment shown in FIG. 26 is illustrated in FIG. 27.When CS2 is brought to a high level from the host side of the CPU or thelike, the memory chip 10 a is transitioned from the DPD mode to astandby state. When the chip enters an operating state according to CS1Bat this time, it performs reading according to an address Ai and outputsread data to DQ. Next, when CS1B is kept at a high level and CS2 becomeslow in level, the memory chip 10 a is brought to a DPD state, so thatcurrent consumption is reduced and the output DQ is brought to highimpedance.

Since the power supply voltage VDD is being applied onto the system evenif the memory chip 10 a is in the DPD state, the ROM is operable.Namely, CEB is brought to a low level so that the ROM is operated.Consequently, the ROM performs reading according to the address Ai andoutputs read data to DQ. While the address Ai for effecting the readingon the ROM is inputted even to the memory chip 10 a in the DPD state atthis time, no current consumption increases because the input circuit 12is deactivated.

While the embodiment shows the case in which the ROM and the memory chip10 a are packaged, no limitation is imposed thereon. For example, aplurality of memory chips 10 a are connected to the address bus Ai, databus DQ and power supply lines VDD and VSS, and the control signals CS2and CS1B are provided every chips in the respective memory chips 10 a,whereby an arbitrary memory chip 10 a of the plurality of memory chips10 a can be selectively brought to the DPD state. Thus, there may alsobe adopted such a configuration that information in which part of amemory area of the system remains in a standby state, is held and othermemory areas are kept in the DPD state, thereby achieving low currentconsumption.

A configurational diagram of one embodiment of a semiconductorintegrated circuit device according to the present invention is shown inFIG. 28. The reference numeral 193 indicates a laminated package, andthe reference numeral 195 indicates a plurality of external terminals.The present embodiment is intended for the case in which thesemiconductor integrated circuit device is made up of a laminatedpackage. For example, a ROM 190 and a memory chip 10 a are mounted orpackaged on a package substrate 194 in an overlapped form. In this case,a laminated structure is formed such that when, for example, the memorychip 10 a is small, such a memory chip small in chip size is providedabove the ROM. Further, the package substrate 194 is connected to eachchip by its corresponding bonding wire 192. The bonding wires 192 serveas the address bus Ai, data bus DQ or power supply lines VDD and VSS andcontrol signal lines.

The DRAM used in a portable device or the like operated by batterydriving as described above needs a reduction in at-standby current in abroad temperature region. Therefore, a refresh cycle is set so that theDRAM intended for such a portable device is capable of holding data evenat such a high temperature as to be adapted to the worst case in thebroad temperature region. However, the inventors of the presentapplication have led to the invention of reducing a refresh currentunder the control of a refresh cycle according to a change intemperature by paying attention to the fact that the portable device orthe like is frequently used in a lower temperature region, particularly,in the neighborhood of normal temperatures at which it is routinelyused.

A block diagram of one embodiment of a refresh timer mounted in a DRAMaccording to the present invention is shown in FIG. 29. In the samedrawing, reference numeral 200 indicates a current source for generatinga current I1 having temperature dependence corresponding to the timerequired to hold information in each memory cell. Although notrestricted in particular, the current source 200 forms a current I1having temperature dependence by using voltages VPG, VBE and VRTR formedby the reference voltage circuit shown in FIG. 17, supplies it to acurrent mirror circuit and outputs it as the form of a bias voltageNBIAS1.

The current I1 generated with the external voltage VDD formed by thecurrent source 200 is transferred to a level converting current source201 in the form of the bias voltage NBIAS1, where it is converted into acurrent 11 with an internal stabilization voltage VDL as the reference.The level converting current source 201 outputs the converted current I1in the form of bias voltages PBIAS and NBIAS formed by a current mirrorcircuit in the same manner. Reference numeral 202 indicates a ringoscillator for producing the current I1 as an operating current inresponse to the bias voltages PBIAS and NBIAS formed by the levelconverting current source 201. Reference numeral 203 indicates a controlcircuit for generating a refresh request signal RF corresponding to theoutput TOUT of the ring oscillator 202.

A circuit diagram of one embodiment illustrative of the current source200 and the level converting current source 201 shown in FIG. 29 isshown in FIG. 30. The constant voltage VPG formed by the referencevoltage circuit is inputted to the gate of a P channel MOSFET 204,whereby the constant current source (MOSFET 109) and current mirrorcircuit of the reference voltage level converting circuit shown in FIG.17 is constituted. Thus, a constant current I1′ equivalent to a constantcurrent I0 hardly having power supply voltage/temperature dependence isobtained. The value of the constant current I1′ is determined by aconstant ratio between the MOSFET 204 and the MOSFET 109 shown in FIG.17. This value will decide the highest operating frequency of the ringoscillator, to be described later. The highest operating frequency has acycle corresponding to an information holding time at the allowablemaximum temperature of each memory cell.

The differential amplifier inputted with the comparing voltage VRTRgenerated in FIG. 17 and the base-emitter voltage VBE of the bipolartransistor 102 obtains a current I1 having temperature dependence.Reference numerals 205 and 206 indicate P channel MOSFETs. The MOSFET205 is inputted a voltage VRTR to its gate and the MOSFET 206 isinputted a voltage VBE to its gate, and the voltages VRTR and VBE arecompared. Here, MOSFETs 207 and 208 function as pure load MOSFETs(resistance means) which do not constitute a current mirror. Since thevoltage VRTR shows that its dependence on the power supplyvoltage/temperature is nearly 0, whereas the voltage VBE shows negativedependence on the temperature, the current I1 shows a characteristicthat decreases with a drop in temperature. This characteristic can beadjusted by changing the level of the comparing voltage VRTR. Thecurrent I1 produced in this way is converted by the current source 201with the internal stabilization power supply VDL as the reference.

The level converting current source 201 is configured such that theconversion into the form of a bias voltage NBIAS1 by the diode-connectedMOSFET 208 through which the current I1 flows, is made, and the samecurrents I1 flow through an N channel MOSFET 211, P channel MOSFETs 209and 210, and an N channel MOSFET 212 provided in a current-mirror form.Owing to the currents I1, the current mirror-configured P channel MOSFET209 and N channel MOSFET 212 outputs them in the form of bias voltagesPBIAS and NBIAS. Such a level converting operation is associated withthe ring oscillator with the current I1 to be described later as anoperating current being operated with VDL for the purpose of its stableoperation.

A circuit diagram depicting one embodiment of the ring oscillator 202shown in FIG. 29 is shown in FIG. 31. Reference numerals 231 through 235respectively indicate inverter circuits that constitute the ringoscillator. P channel MOSFETs 213 through 216 operate a current sourcefor determining a charge current for the inverter circuits 231 through235 in response to the bias voltage PBIAS generated in FIG. 30. Nchannel MOSFETs 217 through 220 operate as a current source fordetermining a discharge-side current for the inverter circuits 231through 235 in response to the bias voltage NBIAS generated in FIG. 30.

Designated at numerals 221 through 230 are respectively load capacitorsfor adjusting the cycle (frequency) of the ring oscillator. Designatedat numeral 240 is a NOR gate circuit for generating a signal OSCSTOPused to stop the oscillator by a power-down signal PD or such a testsignal TSTOP to be described later. Designated at numerals 236 through239 are respectively MOSFETs that constitute NAND gates for stopping theoscillator by the signal OSCSTOP.

Owing to the P channel MOSFETs 213 through 216 and N channel MOSFETs 217through 220, the operating cycle of the present ring oscillator 202 iscontrolled by the current I1 generated by the current source 200 shownin FIG. 30. Thus, the operating cycle has temperature dependence that itextends with a decrease in temperature owing to the temperaturecharacteristic of the current I1, i.e., the cycle becomes long.

A characteristic diagram for describing temperature dependence of therefresh timer according to the present invention is illustrated in FIG.32. When a refresh operation is performed for each operating cycle ofthe ring oscillator 202 or in a cycle equal to several times the cycleby the control circuit 203 shown in FIG. 29, a refresh cycle t extendswith a drop in temperature as shown in the drawing. As a result, arefresh current Iref decreases at a rate of 1/.DELTA.t with the decreasein temperature.

.DELTA.t is adjusted according to a use temperature range. When it isunnecessary to take into consideration a use in an extremely lowtemperature region, for example, the effect of reducing Iref is givenpriority and .DELTA.t is set large. When the use in the extremely lowtemperature region is taken into consideration, there is a possibilitythat the operating cycle t of the ring oscillator 202 will exceed a dataretention characteristic (information holding time). Therefore, .DELTA.tis set in a range having a margin to ensure a data holding operation ofeach memory cell.

A block diagram showing another embodiment of a refresh timer mounted ina DRAM according to the present invention is shown in FIG. 33. Thereference numeral 200 is the current source shown in FIG. 29. Referencenumeral 242 indicates a current source for generating a current I2having no temperature dependence. Reference numeral 243 indicates acurrent source for generating a current I3 by adding the currents I1 andI2. The reference numeral 202 is the ring oscillator shown in FIG. 29.The reference numeral 203 is the control circuit shown in FIG. 29. Inthe present embodiment, such a contrivance that the above considerationof margin on the extremely-low temperature side is made unnecessary, hasbeen carried out. In the present embodiment, a current source 242 forgenerating a current I2 is added to the embodiment shown in FIG. 29, anda current source 243 for forming a current I3 (=I1+I2) obtained byadding a current I1 formed by a current source 200 and the current I2 isprovided as an alternative to the level converting current source 201.The current source 243 is provided together even with a level convertingfunction for converting a VDD-based current to a VDL reference in amanner similar to the current source 201 shown in FIG. 29. The currentsource 242 is one for generating the current I2 low in temperaturedependence on the current I1 of the current source 200. The presentembodiment is similar to the embodiment shown in FIG. 29 in otherconfiguration.

A circuit diagram depicting one embodiment illustrative of the currentsources 200, 242 and 243 shown in FIG. 33 is illustrated in FIG. 34. Thereference numerals 246 to 250 are the same as the current sources 204 to208 shown in FIG. 30. Reference numeral 242 is the same as the currentsource shown in FIG. 33. The current source 242 includes a P channelMOSFET 251 which is inputted a bias voltage VPG to its gate and an Nchannel MOSFET 252 whose gate is connected to its drain terminal, andgenerates a bias voltage BIAS2. Reference numeral 243 indicates acurrent source for adding the current I1 which is generated by thecurrent source 200 and the current I2 which is generated by the currentsource 242 and for generating bias voltages NBIAS and PBIAS. In additionto a current source 200 having temperature dependence similar to FIG.30, a current source 242 is made up of a P channel MOSFET 251 forreceiving a constant voltage VPG, and a diode-configured N channelMOSFET 252 to generate a current I2 having no power supplyvoltage/temperature dependence. The values of the currents I1 and I2formed by the current sources 200 and 242 are determined according to aconstant ratio between the MOSFETs 246 and 251 and the MOSFET 109 shownin FIG. 17.

A bias voltage BIAS1 NBIAS1 corresponding to the current I1 formed bythe current source 200, and a bias voltage BIAS2 NBIAS2 corresponding tothe current I2 formed by the current source 242 are supplied to theircorresponding gates of parallel-configured N channel MOSFETs 255 and 256that constitute the current source 243. A current I3 obtained by addingthe currents I1 and I2 is generated from their common-connected drainsof MOSFETs. A current mirror circuit similar to the above, whichconstitutes the current source 243, forms bias voltages PBIAS and NBIASeach corresponding to the current I3 supplied to the ring oscillator202.

A characteristic diagram for describing temperature dependence of eachcurrent source shown in FIG. 34 is illustrated in FIG. 35. Since thecurrent I1 has temperature dependence as described above, the current I1decreases with the drop in temperature in temperature T1 and T2 regionsshown in the same drawing. Since the current I2 has little temperaturedependence, it shows a substantially constant value in all thetemperature regions T1, T2 and T3.

If the currents are set so as to take I1>>I2 in the high temperatureregion T1, then the current I1 having the temperature dependence becomespredominant over the current I3 for determining the cycle of the ringoscillator 202, and the current I3 decreases with the reduction intemperature in the high temperature region T1 and the medium temperatureregion T2. When the value of the current I1 is lowered with the drop intemperature and reduced to the low temperature region T3 in which thecurrent I2 becomes predominant, the current I3 exhibits a characteristicstable at a constant current in association with the current I2.

A characteristic diagram for describing temperature dependence of therefresh timer shown in FIG. 33 is illustrated in FIG. 36. As is apparenteven from the characteristic diagram shown in FIG. 35, a refresh cycle textends with a drop in temperature in high and medium temperatureregions T1 and T2 but is saturated in a low temperature region T3. Dueto the above characteristic, the refresh cycle is prolonged more thannecessary and hence there is no fear of incurring of data damage. Whilethe effect of reducing a refresh current Iref is not brought about inthe low temperature region T3, current consumption in this region is asfollows. Since a refresh current is reduced and the occupied rate of aDC component is relatively increased, the effect of reducing anat-standby current is not so great even if a refresh operating currentchanges slightly.

A circuit diagram showing another embodiment illustrative of the currentsources 200, 242 and 243 shown in FIG. 33 is shown in FIG. 37. Referencenumeral 500 indicates a current source for generating the current I1having temperature dependence. The current source 500 includes an Nchannel MOSFET 262 that is coupled with a MOSFET 263 whose drain andsource are coupled to each other. Reference numeral 242 a is the currentsource shown in FIG. 37, and reference numeral 243 a is the currentsource shown in FIG. 37. In the present embodiment, a feedback MOSFET262 is added to a differential amplifier of the current source 200. TheMOSFET 262 has the function of feeding back the amount of change incurrent on the comparing voltage VRTR side to the VBE side to therebyfurther increase the amount of change in current I1 with respect to thetemperature. Owing to the feedback effect brought about by the MOSFET262, the amount of change in current increases in the medium temperatureregion T2 in the characteristic diagram shown in FIG. 35.

Namely, the amount of change in timer cycle due to the temperature canbe adjusted by adjusting the constant of the MOSFET 262. Thus, it ispossible to adjust temperature dependence of the timer cycle inaccordance with a data retention characteristic in the mediumtemperature region T2. Accordingly, since the refresh cycle at eachtemperature can be extended to the optimum without incurring datadamage, the effect of reducing a refresh current becomes large.

A circuit diagram showing a further embodiment illustrative of thecurrent sources 200, 242 and 243 shown in FIG. 33 is shown in FIG. 38.Reference numeral 600 indicates a current source for generating thecurrent I1 having temperature dependence. The current source 600includes a current mirror formed with N channel MOSFETs 274 and 275instead of MOSFETs 249 and 250 in the current source 200 shown in FIG.34. Reference numeral 242 b is the current source shown in FIG. 38, andreference numeral 243 b is the current source shown in FIG. 38. Thepresent embodiment is one wherein a load on a differential amplifier ofthe current source 200 is set to a current-mirror type. While the amountof change in current in the medium temperature region T2 is described asa parabola in the characteristic diagram of FIG. 35 in the embodimentsshown in FIGS. 34 and 37, the current can be digitally changed at anarbitrary temperature in the present embodiment.

A block diagram illustrating a further embodiment of a refresh timermounted in a DRAM according to the present invention is shown in FIG.39. Reference numeral 200 is the current source shown in FIG. 33.Reference numeral 242 is the current source shown in FIG. 33. Referencenumerals 201 a and 201 b are similar to the ring oscillator 201 shown inFIG. 29. The current sources 201 a and 201 b as shown in FIG. 39 areprovided in association with these current sources 200 and 242 as shownin FIG. 39. Reference numerals 202 a and 202 b are similar to the ringoscillator 202 shown in FIG. 29, and ring oscillators 202 a and 202 bare controlled by bias voltages formed by the level converting currentsources 201 a and 201 b.

Reference numeral 283 indicates a determination circuit for monitoringoperating states of the two ring oscillators 202 a and 202 b, stopping atimer slow in operating speed by one of signals TSTOP1 and TSTOP2, andmaking effective only one fast in operating speed, of outputs TOUT1 andTOUT2. Reference numeral 284 indicates a control circuit for generatinga refresh request signal RF corresponding to the output TOUT of thedetermination circuit 283.

A characteristic diagram for describing a refresh operation carried outby the refresh timer shown in FIG. 39 is illustrated in FIG. 40. In thepresent embodiment, the current sources and ring oscillators areidentical in configuration to those described up to now. The two ringoscillators 202 a and 202 b operated by currents I1 and I2 of theircurrent sources are selectively operated. Therefore, the output TOUT1 ofthe ring oscillator 202 a shows a characteristic which extends with adrop in temperature as shown in the same drawing, and the output TOUT2of the ring oscillator 202 b exhibits a substantially constantcharacteristic without recourse to the temperature.

If a refresh cycle is determined by the output earlier in operatingcycle at its corresponding temperature, of the outputs TOUT1 and TOUT2,then the final refresh cycle results in a characteristic indicated byTOUT and thereby becomes substantially similar to one shown in FIG. 36.In the present embodiment, the ring oscillators are provided as two sothat a circuit scale is increased correspondingly. On the other hand,the cycles of the ring oscillators 202 a and 202 b can be set to theoptimum in association with temperature regions T1, T2 and T3. In FIG.40, a temperature range is described up to −30.degree. C. to +90.degree.C. The cycle of each ring oscillator can be associated with a refreshcharacteristic of each memory cell over such a wide temperature range.Incidentally, even in the case of a temperature range of from−25.degree. C. to +85.degree. C., it is sufficiently broader than theavailable temperature range of the conventional DRAM. This falls withinthe category of the present invention.

A waveform diagram for describing one example of the operation of therefresh timer shown in FIG. 39 is shown in FIG. 41. The same drawingshows operation waveforms of the refresh timer in the temperature regionT1. When the two ring oscillators 202 a and 202 b are simultaneouslystarted up in the temperature region T1, the output TOUT1 of the ringoscillator 202 a fast in operating speed is outputted ahead of theoutput TOUT2 of the ring oscillator 202 b, and a signal TON1 forrecognizing that TOUT1 has been outputted, is outputted.

In order to prevent the simultaneous stop of the two ring oscillatorsand non-execution of the refresh operation, TON2 is monitored to confirmthat TOUT2 has not yet been outputted. In this state, TSTOP2 isoutputted to stop the ring oscillator 202 b. A refresh request signal RFis outputted for each operating cycle of the ring oscillator 202 a or ina cycle equal to several times the operating cycle. A reset signal RSTis generated from the refresh request signal RF, whereby all the statesare cleared. The same operation is repeated subsequently. Since the ringoscillators 202 a and 202 b are reversed in operating speed in thetemperature region T3, the ring oscillator 202 a is stopped contrary tothe above.

A waveform diagram for describing another example of the operation ofthe refresh timer shown in FIG. 39 is illustrated in FIG. 42. The samedrawing shows operation waveforms of the refresh timer in thetemperature region T2. Since the ring oscillators 202 a and 202 bapproach each other in operating speed in the temperature region T2,there is a possibility that TOUT1 and TOUT2 will be outputtedsimultaneously. Therefore, when their operation recognition signals TON1and TON2 are both outputted, both the ring oscillators 202 a and 202 bare prevented from stopping. A refresh request signal RF is outputted byan AND signal of the two TOUT1 and TOUT2.

A logic circuit diagram showing one embodiment illustrative of theoperation determination circuit 283 and the control circuit 284 shown inFIG. 39 is shown in FIG. 43. Reference numeral 285 indicates a NAND gatefor obtaining a NAND signal TOUT of TOUT1 and TOUT2. NAND gate circuits286 and 287 constitute a latch circuit for recognizing the output ofTOUT1 and outputting TON1. NAND gate circuits 288 and 289 constitute alatch circuit for recognizing the output of TOUT2 and outputting TON2.

Reference numeral 292 indicates a NOR gate for monitoring TON1 and TON2and outputting TSTOP1. Reference numeral 293 indicates a NOR gate formonitoring TON1 and TON2 and outputting TSTOP2. Gate circuits andinverter circuits 296 to 306 constitute a shift register for countingTOUT. A delay circuit 308 and a gate circuit 307 constitute a circuitfor generating a one-shot pulse for RST from a refresh request signalRF. Reference numerals 294 and 295 indicate a NAND and an INVERTER gatecircuit for generating a one-shot pulse for RST from a power-down signalPD and a one shot signal from the gate circuit 307. Reference numeral308 indicates a delay circuit for generating a one-shot pulse from therefresh request signal RF.

A block diagram showing a still further embodiment of a refresh timeraccording to the present invention is shown in FIG. 44. In the presentembodiment, a refresh request stop mode is added. Namely, in a memory inwhich data retention is done with an internal refresh timer, a truecharacteristic is not obtained because a refresh operation is carriedout by the internal refresh timer even upon measuring a data retentioncharacteristic. In the present embodiment, a refresh operation stopsignal TREFOFFB is provided so as to avoid the reception of a refreshrequest signal RF.

In the present embodiment, external control for a refresh operationcycle and a refresh request stop mode function are added. The referencelabel RAOT indicates a refresh request signal which is selected from therefresh request signal RF generated from a refresh timer 308 a and anexternal refresh request signal EXTRF by a selector 400. If the refreshoperation can be externally controlled, then current consumption in anarbitrary refresh operation cycle can be recognized. It is also possibleto obtain data effective for setting of the characteristic of eachrefresh timer described up to now. In the memory in which the dataretention has been carried out by the internal refresh timer, therefresh operation is done by the internal refresh timer even uponmeasuring the data retention characteristic. Therefore, a mode forstopping a refresh request is required.

In order to cause the refresh timer to have such a function as describedabove, the following circuits are added to a refresh timer 308 a.Reference numeral 403 indicates a bonding pad for inputting a refreshrequest signal from outside. Reference numeral 309 indicates an inputbuffer for taking in or capturing a refresh request signal inputted fromthe bonding pad 403. Designated at numeral 308 a is such a refresh timeras described above. Reference numeral 400 indicates a selector forselecting a signal RF outputted from the refresh timer 308 a and asignal EXTRF outputted from the input buffer 309 in response to a selectsignal TREFC.

Reference numeral 401 indicates a NAND gate for invalidating an outputSRF of the selector 400 in response to a signal TREFOFB and stopping arefresh startup signal RACT. The bonding pad 403 may share the use of apad used in a normal operation, such as a dedicated pad or an addresspin or the like. The signals TREFC and TREFOFB are generated accordingto a test mode or inputted from outside through a dedicated pad.

Operations and effects obtained from the above-described embodiments areas follows:

(1) An advantageous effect is obtained in that a semiconductor memorycircuit can be obtained which includes an internal circuit capable ofselectively stopping the supply and stop of an operating voltage viaswitch means and wherein the supply and stop of the operating voltage bythe switch means are controlled by an input circuit having apredetermined control signal therein to thereby realize a reduction inpower consumption by virtue of a reduction of a DC current and a leakcurrent when no memory operation is done.

(2) In addition to the above, an advantageous effect is obtained in thatan output circuit for forming an output signal in response to a signaloutputted from the memory array is operated on a steady basis by theoperating voltage, and the input circuit brings the output circuit to anoutput high impedance state when the switch means is brought to an offstate to stop the supply of the operating voltage to the internalcircuit, whereby the semiconductor memory circuit is connected to othercircuit blocks and a common bus, thereby making it possible to bringonly the semiconductor memory circuit to the low power consumption mode.

(3) In addition to the above, an advantageous effect is obtained in thatthe memory array comprises memory cells each of which needs a periodicor cyclic refresh operation for holding memory information, whereby areduction in power consumption can be realized while a great increase instorage capacity and high integration are being achieved.

(4) In addition to the above, an advantageous effect is obtained in thatthe internal circuit is provided with an operation voltage generatingcircuit for supplying an operating voltage to an address selectioncircuit for performing the operation of selecting each memory cell, andthe operation voltage generating circuit performs the supply and stop ofan operating voltage supplied from an external terminal via the switchmeans, whereby the switching between the supply of an operating voltageto the internal circuit and its stop can be done in a simple circuitconfiguration.

(5) In addition to the above, an advantageous effect is obtained in thata semiconductor memory circuit is adopted which includes a timemultimode for, when a memory operation for reading or writing memoryinformation from and to each of the memory cells and a refresh operationbased on addressing different from that at the memory operation competewith each other on a time basis, executing a time multimode forexecuting the refresh operation before or after such a memory operation,and an interface is associated with a static RAM, whereby asemiconductor memory circuit having mass storage capacity comparable toa dynamic RAM can be implemented while realizing low power consumptionand an easy-to-use memory operation comparable to the static RAM.

(6) An advantageous effect is obtained in that in a semiconductor memorycircuit including memory cells each of which needs a periodic or cyclicrefresh operation for holding memory information, the cycle of therefresh operation is changed according to temperature dependence of aninformation holding time of each memory cell to thereby make it possibleto greatly reduce current consumption necessary for the refreshoperation.

(7) In addition to the above, an advantageous effect is obtained in thata first temperature region in which the cycle is changed according to aninformation holding time of each memory cell on the high temperatureside in which a refresh cycle is relatively shortened, and a secondtemperature region in which the cycle is set to a substantially constantcycle shorter than an information holding time of each memory cell onthe low temperature side in which a refresh cycle is relatively madelong, are provided, whereby current consumption necessary for therefresh operation can be significantly reduced while a data holdingcharacteristic in a low temperature region is being maintained.

(8) In addition to the above, an advantageous effect is obtained in thatwhen a memory operation for reading or writing memory information fromand to each of the memory cells and a refresh operation based onaddressing different from that at the memory operation compete with eachother on a time basis, a time multimode for executing the refreshoperation before or after such a memory operation is set, and aninterface circuit corresponding to a static RAM is provided, whereby asemiconductor memory circuit having mass storage capacity comparable toa dynamic RAM can be realized while implementing low power consumptionand a memory operation replaceable by the static RAM.

(9) In addition to the above, an advantageous effect is obtained in thatthe refresh operation is controlled by a timer circuit using the cycleof an oscillator circuit operated by a current obtained by combining afirst current having temperature dependence corresponding to the firsttemperature region and a constant current corresponding to the secondtemperature region, whereby current consumption necessary for therefresh operation can be significantly reduced while maintaining a dataholding characteristic in a low temperature region.

(10) An advantageous effect is obtained in that as a timer circuit forcontrolling the refresh operation, a first oscillator circuit operatedby a first current having temperature dependence corresponding to afirst temperature region, and a second oscillator circuit operated by aconstant current corresponding to the second temperature region areprovided, and the timer circuit comprises an output selection circuitfor forming the refresh control signal according to a short one ofoscillation outputs of the first oscillation circuit and the secondoscillation circuit, whereby current consumption necessary for therefresh operation can be significantly reduced while maintaining a dataholding characteristic in a low temperature region.

(11) In addition to the above, an advantageous effect is obtained inthat the operation of the timer circuit is invalidated so that theinformation holding time of each memory cell is capable of beingmeasured according to the memory operation, whereby a truecharacteristic can be evaluated upon an analysis of AC and DC currentcomponents of an at-standby current in a cut and divided state, ananalysis intended for a further current consumption reduction with theextension of a refresh cycle, and evaluation of a data retentioncharacteristic.

While the invention made above by the present inventors has beendescribed specifically by the illustrated embodiments, the invention ofthe present application is not limited to the embodiments. It isneedless to say that various changes can be made thereto within thescope not departing from the substance thereof. For example, as a memoryarray, may be used one wherein it is divided into plural form in bitline and word line directions and a plurality of address selectioncircuits are provided in association with such divided memory cellarrays. As word lines and bit lines, may be ones which adopt ahierarchical word line system, like main and local word lines. The bitlines may also adopt a hierarchical bit line system, like local and mainbit lines or the like.

The memory cell arrays and the address selection circuits can beconfigured by using the device structure and circuit layout technologyemployed in the dynamic RAM known to date. As in this embodiment, asynchronous pseudo SRAM having a refresh concealment+page mode, and arefresh concealment+DRAM interface (address multi and RAS/CAS control)can also be configured.

With high functioning of electronic apparatus like a cellular telephoneor the like, there has been increasingly a demand for a large-capacitywork RAM. While the work RAM is normally fabricated as an asynchronousSRAM, it is not suited for an increase in capacity. While attention hasbeen given to a large-capacity DRAM as its alternative memory, it needsrefresh and has poor usability. A semiconductor memory device accordingto the present invention is capable of holding compatibility with theasynchronous SRAM and is formed integrally with a flash memory. Thus,the semiconductor memory device can exhibit various memory operationsaccording to a combination with the flash memory having a non-volatileinformation function at power-off.

Even in a non-volatile memory like a flash memory or the like inaddition to the DRAM like the pseudo SRAM, pseudo synchronous SRAM orthe like that needs the refresh operation described above, such acircuit made up of MOSFETs each having a low threshold voltage that anoperating current always continues to flow by a charge pump circuit or aleak current produced by each MOSFET is innegligible, increases incurrent consumption upon its non-operation. Therefore, a semiconductormemory circuit can be brought to low power consumption by theapplication of the present invention thereto.

Before the transition to the DPD mode, only the refresh operation may bestopped by the timer circuit for a predetermined period. Namely, therefresh timer 14 is deactivated by the CS2 signal as a first stage. Thisis defined as a first mode for reducing the refresh operating currentshown in FIG. 25. The timer circuit determines that the first mode hascontinued for a predetermined period, and the mode may be transitionedto the DPD mode for reducing the MOS off current and power supplycircuit DC current. Since the refresh operation has simply stoppedduring a period of the first mode in this configuration, the stored datais damaged but a write operation can be performed immediately. It isthus possible to ensure high response.

The present invention can be widely used in ones multichip-configured asin the embodiments in addition to a single memory device or the like, orvarious semiconductor memory circuits including a semiconductor memorycircuit formed in a semiconductor integrated circuit device like asystem LSI equipped with a CPU, a RAM, a DRAM, etc.

Advantageous effects obtained by a typical one of the inventionsdisclosed in the present application will be described in brief asfollows. A semiconductor memory circuit can be obtained wherein aninternal circuit is provided which is capable of selectively the supplyand stop of an operating voltage via switch means, and includes a memoryarray, and an input circuit receiving a predetermined control signaltherein controls the supply and stop of the operating voltage by theswitch means, whereby low power consumption is realized by a reductionof a DC current and a leak current when no memory operation isperformed.

1. A semiconductor circuit apparatus, comprising: a first input meansfor receiving a first power supply voltage and a first signal andoutputting an internal signal; a second input means for receiving thefirst power supply voltage and a control signal; a first processingmeans for outputting a second signal in response to the control signal;an output means for outputting an output signal based on the secondsignal; and a power supply means for receiving the first power supplyvoltage and the internal signal, and for supplying an operation voltageto the first processing means, wherein the first signal instructs afirst mode which stops supplying the operation voltage from the powersupply means to the first processing means, and wherein the output meansis brought to an output high impedance state in response to the internalsignal in the first mode.
 2. The semiconductor circuit apparatusaccording to claim 1, wherein the first mode is a low power consumptionmode.
 3. The semiconductor circuit apparatus according to claim 1,wherein the power supply means comprises: an operation voltagegenerating circuit which supplies the operation voltage to the firstprocessing means; and a switch circuit which receives the first powersupply voltage and supplies the first power supply voltage to theoperation voltage generating circuit in response to the internal signal.4. The semiconductor circuit apparatus according to claim 1, wherein thefirst processing means comprises: a memory array comprising a pluralityof word lines, a plurality of data lines, a plurality of memory cellsrespectively connected to the plurality of word lines and the pluralityof data lines; and a word line drive circuit connected to the pluralityof word lines, and wherein the operation voltage is a voltage fordriving the word line drive circuit.